This invention relates generally to methods for reducing dental sensitivity resulting from exposed dentin that has lost its natural coverings of enamel or cementum.
Many patients complain of tooth sensitivity to hot and cold drinks and to certain acidic or hypertonic foods. This sensitivity often occurs when gum tissue recedes from the necks of teeth, exposing root surfaces that are not covered by hard enamel but by soft cementum. The cementum is so thin and soft that it can be removed by tooth brushing, thereby exposing the sensitive underlying dentin. The dentin can also become exposed under restorations. The pain that patients feel from exposed dentin is called dentin sensitivity, as reported in Pashley, Arch Oral Biol 39 (Suppl) 735-805 (1994).
Dentin sensitivity, whether on exposed surfaces at the necks of teeth or under restorations, is reportedly due to minute fluid shifts across dentin in response to painful stimuli (Brxc3xa4nnstrxc3x6m, Oper Dent 9: 59-68, 1984). This theory, called the hydrodynamic theory, (Brxc3xa4nnstrxc3x6m and Astrxc3x6m, Int Dent J 22: 219-j226, 1972), assumes that fluid can move within or through the microscopic tubules making up dentin, at a rate that activates mechanoreceptor nerves in the dentin pulp. A corollary to this theory is that anything that decreases the ease with which fluid can move across dentin should decrease dentin sensitivity (Pashley, J Endodont 12: 465-476, 1986). A number of agents have been previously screened for their ability to occlude dentinal tubules, including potassium oxalate (Greenhill and Pashley, J Dent Res 60: 686-698, 1981). When 3% w/v acidic monopotassium-monohydrogen oxalate is applied to dentin, the hydraulic conductance of dentin is reduced both in vitro and in vivo (Pashley, J Endodont 12: 465-476, 1986). It has been reported that the soluble oxalate reacts with ionized calcium in dentinal fluid or on dentin to form insoluble crystals of calcium oxalate. U.S. Pat. No. 4,057,621. Compositions and uses of solutions and gels that contain concentrations of neutral and acidic monopotassium-monohydrogen oxalates are outlined in U.S. Pat. Nos. 4,057,621 and 4,538,990. Although such treatments have been shown to decrease dentin sensitivity clinically (Konttari-Nxc3xa4rhi, Ph.D. thesis, University of Kuopio, Kuopio, Finland, 1993), the crystals have a finite solubility, and can solubilize from the dentin surface within one week (Kerns et al., J Periodont 62: 421-428, 1991). Moreover, because the crystals are on the surface, patients can remove them by daily brushing, and thereby cause a recurrence of dentin sensitivity.
Adhesive resin monomers have also been advocated for treating dentin sensitivity. (Yoshiyama, Proc Finn Dent Soc 88 (Suppl 1) 337-344, 1992; Tavares, J Am Dent Assoc 125: 1337-1342, 1994). Such adhesives protect the dentin by forming a thin layer (ca 20-50 xcexcm thick) on the surface of the dentin. Because of their limited strength, and their thinness, adhesive resins can generally be easily removed from the dentin surface by daily brushing.
Recent improvements in resin adhesives include the development of monomers that are much more hydrophilic, unlike previous versions that were hydrophobic. This property permits resin monomers to penetrate water-filled tubules where they can form resin-droplets or micelles or even solid resin tags that penetrate into the tubules and bond to the walls of the tubules (Tay et al., Cells and Mater 4: 317-329, 1994). Under these conditions, it is the resin tags that actually occlude the tubules. However, many polymers obtained from these monomers have a coefficient of thermal expansion that is much higher (71-94xc3x9710xe2x88x926/xc2x0 C.) than that of dentin (11.4xc3x9710xe2x88x926/xc2x0 C., Craig, Restorative Dental Materials, 9th ed., Mosby, St. Louis, p. 43, 1993). Cold foods and liquids may cause the resin tags to shrink, allowing movement of dentinal fluid around them at a rate that may cause pain. Moreover, the resin often shrinks during polymerization, producing only partial tubule occlusion.
Thus, neither oxalates nor resins have proven completely effective to reduce dentin sensitivity for a prolonged period of time. Moreover, it has also been reported that the combination of oxalate and resin is not effective to reduce dentin sensitivity for a prolonged period of time, because the adhesive resins do not bond well to oxalate-treated dentin. (Pashley, Tao and Pashley, Am J Dent 6: 116-118, 1993). This is due to the physical presence of crystals of calcium oxalate on the dentin surface that prevents an intimate attachment of the resin to the underlying dentin surface. What is needed, therefore, is a method of reducing dentin sensitivity for a prolonged period of time, and that withstands the abrasive effects of regular brushing.
The above disadvantages of the prior art are overcome by the present invention which relates to a method of reducing dentin sensitivity for extended periods of time by acid pre-treating the dentin surface before applying an acidic oxalate to the dentin surface. The resulting dentin is substantially less subject to dentin sensitivity, and the treatment endures for a prolonged period of time. The resulting dentin is also substantially more receptive to bonding agents which can be applied over the oxalate-treated dentin to obtain an even more durable and prolonged treatment.
Thus, in accordance with the purpose(s) of this invention, as embodied and broadly described herein, this invention in one aspect relates to a method of reducing dentin sensitivity comprising: applying an effective amount of an acid to a dentin surface to form a treated surface; and administering an effective amount of an acidic oxalate to the treated surface so as to occlude dentinal tubules beneath the dentin surface. The method may optionally comprise the subsequent application of a suitable bonding agent.
Another aspect of the invention provides a kit for the treatment of dentin sensitivity, comprising a first container of an acid treatment composition, and a second container of an acidic oxalate composition. The kit may also comprise a suitable bonding agent.
Additional aspects and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.